Find exactly how many litres or gallons to remove and replace.
Open live calculator →A 25% change on a 160 litre aquarium requires 40 litres of replacement water.
This is the amount to remove and replace.
Turn a planned water-change percentage into a practical bucket volume using the aquarium's real water capacity.
The live tool updates immediately and shows the result in the units commonly used by aquarium keepers around the world.
Use net rather than advertised tank volume.
Match replacement-water temperature appropriately.
Prepare conditioner or minerals according to their labels.
A common baseline is 20–30% weekly for a stocked community tank. Heavily stocked or heavily fed tanks may need more frequent changes; lightly stocked planted tanks can often run leaner.
Large changes are safe when the new water is temperature-matched and dechlorinated, and its hardness is similar. Sudden parameter swings—not the volume itself—are what stress fish.
Real (net) water volume. A "25% change" measured against the advertised tank size removes a larger true fraction in a heavily scaped tank than intended.